The purpose of the proposed study is to investigate the long-term usefulness of stimulant medication in the treatment of attention deficit disorder, residual type (ADD,RT). Placebo-controlled studies conducted by our group have found that methylphenidate produces moderate-to-marked benefit in approximately 60-70% of patients with ADD,RT. Anecdotal clinical data suggest that tolerance to stimulant mediation does not develop, that mediation continues to control target symptoms and that continued use of medication is associated with substantial vocational, personal and academic gains. The proposed study has been designed to test these observations. Approximately 160 patients with ADD,RT will be screened in a double-blind trail of methylphenidate. The 100 individuals manifesting moderate-to-marked improvement (operationally defined) will be entered into a long-term trial. A variety of instruments will be employed periodically for at least 24 months in order to monitor the symptomatic progress and social and vocational function of the subjects. In order to determine continuing need for medication after 12 months of treatment, one-half the sample will receive a double-blind period of discontinuation. At this time medication will gradually be reduced and discontinued, which will test for the persistence of target symptoms (as opposed to stimulant-withdrawal effects). Subjects whose ADD,RT problems recurred would be placed back on active medication. The overall design is to determine (1) if tolerance develops to stimulant medication and (2) if long-term treatment is necessary. An additional feature of the proposal will be the psychiatric and social follow-up of the approximately 60 patients diagnosed with ADD,RT who are not treatment responders. Such a follow-up may provide information about the natural history of this subgroup of patients with putative ADD,RT.